This invention pertains to a method and apparatus for the treatment of potable water supplies. More particularly, the invention pertains to the use of solid calcium hypochlorite as a disinfecting agent for the treatment of municipal water supplies.
Municipal water production facilities currently use chlorine gas as the primary disinfectant. In October, 1992, chlorine was reclassified by the United States Department of Transportation (DOT) from a non-flammable gas to a poison-inhalation hazard. This reclassification results in transportation restrictions. A vehicle transporting hazardous materials such as chlorine must not be parked on or within five feet of the traveled portion of public street or highway except for brief periods when the necessities of operation require the vehicle to be parked and make it impracticable to park the vehicle in any other place. Unless there is no practicable alternative, a motor vehicle which contains hazardous materials must be operated over routes which do not go through or near heavily populated areas, places where crowds are assembled, tunnels, narrow streets, or alleys.
In response to these regulatory requirements, distributors of chlorine have determined that they cannot meet the regulatory requirements and therefore, are unwilling to make such deliveries.
In addition to increased regulations governing the transportation of chlorine, the United States Uniform Fire Code requires that each chlorine system be designed to handle the accidental release of gas from the entire contents of the largest single source of gas (Uniform Fire Code Sections 80.301-80.306). The cost of installing such equipment at municipal production well sites is excessive. With mounting restrictions on transporting, handling, and storing chlorine gas, it is important that alternative methods of disinfection be developed for municipal water production facilities.
One alternative method of disinfection is liquid sodium hypochlorite (NaOCl). However, upon investigation, a number of disadvantages of this disinfectant have been discovered. Sodium hypochlorite is not very stable at the solution concentrations typical for water disinfection. During storage, this instability results in a loss of strength within a few weeks. In addition, along with the product degradation, chlorites and chlorates are formed. It is believed that in the future, United States Environmental Protection Agency (EPA) regulations may control these disinfection byproducts.
It is, therefore, desirable to provide a method and apparatus for treatment of potable water which does not use chlorine gas or liquid sodium hypochlorite.
Solid calcium hypochlorite (Ca(OCl).sub.2) is not subject to the aforementioned transportation restrictions and has the advantage that it has a shelf life of over two years during which time the chemical retains its full strength. More specifically, calcium hypochlorite can be shipped as a relatively stable solid containing 70% or more available chlorine.
Solid calcium hypochlorite is commonly utilized to treat swimming pools. In conventional methods of application in swimming pools, tablets are placed in the pool skimmer or in dissolving baskets around the pool. The level of residual chlorine is not easily controlled with these approaches and therefore they are not suitable for application to the production of potable water.
In addition to the basket and skimmer devices, other devices have in the past been developed for using solid soluble material for treating water. Several such devices are discussed in U.S. Pat. No. 3,802,845. However, these prior devices, as well as the one described in the '845 patent, are not suitable for use in water production operations.
Apparatus which has been designed for use with solid calcium hypochlorite are commercially available but are not insertable into a pressurized system. Typical solid calcium hypochlorite feeders utilize a pump on the outlet of the feeder to pump the chlorine solution formed from the solid calcium hypochlorite. These chlorinators have the further disadvantage that the influent to the device would have to exactly match the effluent flow capacity of the pump. Otherwise, cavitation occurs in the pump or flooding of the chlorinator could occur. If flooding occurs in the chlorinator, the solid calcium hypochlorite liquefies. In addition, calcium buildup occurs in the pump impeller housing resulting in impeller or seal damage.
In the prior systems, batches of chlorine solution are produced from the solid calcium hypochlorite and the batch is pumped into the water.
It is therefore one object of the invention to provide a method and apparatus for the treatment of potable water which will not require the use of chlorine gas or other hazardous material.
It is a further object of the invention to provide a method and apparatus for treatment of potable water utilizing an unpressurized chlorinator tank.
It is yet another object of the invention to provide a method and apparatus for the treatment of potable water in which maintenance of the apparatus is reduced.